Therapeutic devices, and more specifically, osteogenic devices, typically are sterilized prior to implantation in an intended recipient. Sterilization is required to ensure that the devices do not introduce potential pathogens, or other biologically infectious agents into the intended recipient. Osteogenic devices comprising an osteogenic protein in combination with an insoluble carrier material are useful for inducing bone formation at a preselected locus, e.g., at a site of a bone fracture, in a mammal. Heretofore, the carrier material and osteogenic protein typically have been sterilized separately and then combined to produce a sterile implantable device. This method, however, cannot guarantee the sterility of the resulting device.
The most desirable method for sterilizing a device comprising two or more components is by a process, referred to in the art as "terminal sterilization". By this process, the device is sterilized following formulation, i.e., after all the components have been combined with one another in the device. A variety of physical or chemical methods have been developed for use in terminal sterilization and include, for example, exposure to chemicals or heat, or exposure to ionizing or non-ionizing radiation. These methods, however, can have inherent problems.
For example, chemical reagents useful in chemical sterilization, or the reaction byproducts, can be harmful to the intended recipient. Accordingly, such chemicals must be removed prior to implantation of the devices. Ethylene oxide and formaldehyde are reagents commonly used as sterilization reagents. However, both are alkylating agents and therefore can modify and inactivate biologically active molecules. In addition, both of these chemicals are carcinogens and mutagens (Davis et al., (1973) "Microbiology, 2nd Ed.", Harper and Row, Publishers). Similarly, where the device requires a biologically active protein, exposing the device to elevated temperatures is not desirable because the proteins can be denatured and subsequently inactivated by exposure to heat. Although the sterilization of objects by exposure to ionizing and non-ionizing radiation obviates the necessity of adding potentially toxic chemicals, the radiation energy and/or its byproducts, including oxygen free radicals, are competent to modify protein conformation and so can damage or inactivate the protein, In addition, exposure of some medically important polymers, for example, as polyurethane or polymethylmethacrylate to gamma radiation can result in immediate and long term physical changes to the polymer.
It is therefore an object of this invention to provide a terminally sterilized osteogenic device which, when implanted at a preselected locus in a mammal, is capable of producing bone at the locus. Another object is to provide a general process for terminally sterilizing osteogenic devices without compromising the biological activity and/or biocompatibility of the device. Another object of the invention is to provide a method of inducing bone formation at a preselected locus in a mammal using a terminally sterilized device of the invention.
These and other objects and features of the invention will be apparent from the description, drawings, and claims which follow.